The purpose of this study is to determine the effect of two endotracheal suctioning (ETS) techniques, off vs. on ventilator ETS (Ballard Trach Care System) on cardiopulmonary status in acutely ill adults. The specific aims of this study are to determine the effect of hyperoxygenation (FIO.2 1.0) via a ventilator (vent) followed by off vs. on vent ETS and 2 vs. 3 hyperoxygenation-suction (H-S) sequences on systolic and diastolic arterial pressure, mean arterial pressure (MAP), heart rate (HR) and rhythm, airway pressure (Paw), arterial blood gases (ABG's) and secretion recovery (SR) in acutely ill adults. The sample will consist of 60 M & F intubated and mechanically ventilated patients who meet specific criteria. Each of the subjects will be exposed to the following randomly ordered (Latin Square Design) treatments once each hour for four consecutive hours: 1) 3 H-S followed by off vent ETS, 2) 3 H-S followed by on vent ETS, 3) 2 H-S followed by off vent ETS, 4) 2 H-S followed by on vent ETS. The subjects will be hyperoxygenated at FIO.2 1.0 with four breaths at 135% of prescribed tidal volume in 20 secs. via their vent. Immediately following hyperoxygenation, the subjects will be suctioned (flow rate 16L/min) continuously for 10 secs. with a 14 French catheter either off the vent or on the vent. The effects of off vs. on vent ETS on systolic and diastolic arterial pressure, MAP, Paw, HR and rhythm will be monitored continuously by a calibrated graphic recorder (Gould 2800), stored on magnetic tape (Hewlett-Packard), and later analyzed using ASYST software. The effects of hyperoxygenation followed by off vs. on vent on ABG's (Corning 158) and oxygen saturation (Physiocontrol) will be monitored. SR will be determined by pre and post weight in grams using the Mettler balance. The data will be analyzed using ANOVA for repeated measures to determine the effect of off vs. on vent ETS and 2 vs. 3 H-S sequences on the selected physiological variables. The results of this study will determine the effect of the two techniques on cardiopulmonary parameters and provide data for the establishment of safe ETS protocols in acutely ill adults.